Aromatic phosphates are known to be useful as flame retardant agents and plasticizers for thermoplastic polymers and blends, such as compositions of polyphenylene oxide and polystyrene. Various methods for preparing aromatic phosphates (also referred to herein as aryl phosphates) have been described or proposed. For instance, triarylphosphites can be produced by the reaction of phosphorus trihalides, for example, PCl.sub.3, with hydroxy-substituted aromatic compounds in the presence of a catalyst (Maul, et al., U.S. Pat. No. 4,312,818) and it is known that, analogously, triarylphosphates can be prepared from the reaction of phosphoryl halides, e.g., POCl.sub.3, with hydroxy-substituted aromatic compounds. Other procedures involve the reaction of a phenolic compound with a pentavalent phosphorus compound, e.g., P.sub.2 O.sub.5, or phosphoric acid, as disclosed in British Pat. No. 763,311, and of a phenolate with a pentavalent phosphorus compound as disclosed in U.S. Pat. No. 2,886,586.